U.S. Pat. No. 4,508,842 discloses a highly active vanadium-containing catalyst capable of producing ethylene polymers having a broad molecular weight distribution. Said catalyst comprises:
(A) a solid catalyst precursor consisting essentially of PA1 (B) an alkylaluminum cocatalyst, and PA1 (C) a halohydrocarbon polymerization promoter. PA1 (1) a solid catalyst component obtained by precipitating vanadium trihalide from an ether solution onto a silica and/or alumina carrier and then treating the product with an alkylaluminum, PA1 (2) an alkylaluminum, PA1 (3) an alkyl halide, and PA1 (4) an alkoxy compound of silicon. PA1 (A) a solid catalyst precursor consisting essentially of PA1 (B) an alkylaluminum cocatalyst, and PA1 (C) a halohydrocarbon polymerization promoter, PA1 R is a monovalent hydrocarbon radical free of aliphatic unsaturation containing from 1 to 14 carbon atoms, PA1 R.sup.1 is a monovalent hydrocarbon radical free of aliphatic unsaturation containing from 1 to 14 carbon atoms, and PA1 n is an integer having a value of from 1 to 4. PA1 (A) a solid catalyst precursor consisting essentially of PA1 (B) an alkylaluminum cocatalyst, and PA1 (C) a halohydrocarbon polymerization promoter.
(1) an inorganic carrier, as support for PA2 (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, and PA2 (3) a boron halide or alkyl-aluminum modifier, PA2 (1) a solid, particulate, porous, inorganic carrier, as support for PA2 (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, and PA2 (3) a boron halide or alkyl-aluminum modifier, PA2 (1) a solid, particulate, porous, inorganic carrier, as support for PA2 (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, PA2 (3) a boron halide or alkyl-aluminum modifier, and PA2 (4) an silicon-containing molecular weight distribution (MWD) regulator having the formula (RO).sub.n SiR.sup.1.sub.(4-n), wherein R, R.sup.I and n are as defined above,
The polymers produced in accordance with U.S. Pat. No. 4,508,842 have a relatively broad molecular weight distribution, and excellent extrudability. These properties render them extremely useful in a wide variety of applications, such as wire and cable insulation, blow molding, film, and pipe fabrication. However, such polymers cannot be used in other applications, such as injection molding, which require a narrower molecular weight distribution.
Japanese Public Disclosure No. 62-25112 (Application Ser. No. 60-163525), on the other hand, discloses vanadium-containing catalyst compositions useful in the preparation of ethylene polymers having a narrow molecular weight distribution. Such compositions consist of:
While the catalyst compositions prepared in this manner have been found useful in the preparation of polymers having a narrow molecular weight distribution, the presence of alkoxysilicon compounds in such compositions has been found to adversely affect polymer productivity.